Our project continues to focus on the properties and dynamics of cellular membranes involved in the secretory process of the exocrine pancreas. Several lines are to be followed: (1) Specific lectins for 6 saccharides, each coupled to ferritin, will be used to complete the topographic mapping of exocrine, endocrine and duct cell plasmalemma and extended to examine the course of differentiation of the surface of the progenitor cell during cytodifferentiation. (2) Lectins will be used as probes for dynamic changes in the apical plasmalemma during exocytosis and will be assayed for their effect on exocytosis with the aim of determining if secretagogue receptors are glycoproteins. (3) Photoactivatable peptide secretagogues and antihormone antibodies will be applied to exocrine cells to determine the topographic distribution of receptors on the cell surface and the effects of receptor redistribution on function. (4) Correlations between onset of hormone responsiveness in exocrine cells and appearance of adenylate and guanylate cyclase activities will be made on cultures of differentiating exocrine cells. (5) The role of cGMP in regulation of exocytosis will be examined. BIBLIOGRAPHIC REFERENCES: Galardy, R.E. and J.D. Jamieson. Photoaffinity labeling of secretagogue receptors in the pancreatic exocrine cell. In Gastrointestinal Hormones, a Symposium (James C. Thompson, ed.) University of Texas Press, Austin, Texas. 345-365, 1975. Jamieson, J.D. Membranes and Secretion. In Cell Membranes. (G. Weismann and R. Claiborne, eds.). HP Publishing Co., Inc., New York, 143-152, 1975.